The present invention relates generally to support systems used in the construction industry, and more particularly to ladder-type cable trays used to support runs of cable (e.g., bundles of electrical wiring and the like).
Conventional ladder-type cable trays comprise spaced apart parallel and/or concentric side rails and a series of spaced-apart rungs extending transversely between the rails, the rails and rungs typically being of extruded aluminum alloy or other suitable formed metal. It has been the conventional practice to secure the rungs to the side rails by welding. Some cable tray systems use screw fasteners as disclosed in U.S. Pat. No. 5,580,014 to Rinderer (incorporated herein by reference).
Cable trays come in various widths and have straight sections and curved sections with various bend angles (e.g., 45.degree., 90.degree.) and radii of curvature. To provide for ease of design, construction and installation, these dimensions and configurations have been standardized. In a curved (arcuate) section of cable tray the rungs extend, preferably radially, between the side rails and need to be accurately positioned to control spacing between the rungs. If the rungs are attached to the rails by mechanical fasteners (e.g., screws), accurate rung spacing requires accurately spaced apertures for receiving the fasteners. Heretofore, the spacing between these apertures has varied according to the width of the tray, its radii of curvature and its bend angle. This variation in spacing reduces manufacturing flexibility and efficiency and increases cost. Therefore, for this type of cable tray there is a need for a construction which uses a standardized fastener hole spacing which will accommodate a wide variety of tray sizes and configurations.